Electron spectroscopy for chemical analysis studies were carried out on CuOx films deposited onto yttria-stabilized zirconia single-crystal substrates by electron-beam evaporation under molecular beam epitaxy conditions. The measurements were taken without exposing the films to the atmosphere. The results show that copper oxide dissociates under electron-beam heating in high vacuum and the reassociation of copper and oxygen to form suboxide (CuOx) at the substrate is a function of its temperature. The maximum oxygen content was found to be about 46% of the starting source material at the growth temperature of 500 degrees C, above which the CuOx film starts to decompose.